When this data updates
Every figure on this site carries its vintage. This page says when each vintage is replaced. Data last rebuilt 30 August 2026.
The publication calendar
| Product | Published | What it changes here |
|---|---|---|
| County population estimates | Annually, in March | Population, growth since 2020, births, deaths, net migration, density, and every ranking built on them |
| Subcounty population estimates | Annually, in May | Largest city per county |
| American Community Survey 5-year | Annually, in December | Median household income, median home value, median age, households, housing units |
| Cartographic boundary files | Annually, in spring | Every map on the site, and the downloadable map files |
| Gazetteer files | Annually, in autumn | Land and water area, and the density computed from it |
| County adjacency file | Irregularly | Bordering counties and shared border lengths |
| Decennial Census | Every ten years | Resets the base for the entire estimate series |
How a refresh is handled
The data pipeline is run by hand, not during the site build. It fetches each source, checks the record counts against what we expect, joins everything on the five-digit GEOID, and refuses to write anything at all if a check fails. The output is committed to version control, so a refresh appears as a reviewable diff of every changed figure before it goes live.
That is deliberately slower than fetching live. It means the site cannot silently ship a truncated download or a source that changed shape overnight, and it means a deploy never fails because a government server happens to be down.
When the geography itself changes
County boundaries and identifiers are not static, and this is where most county datasets quietly break.
- 2022: Connecticut's eight counties were retired and replaced by nine planning regions with new codes. Any dataset still showing eight Connecticut counties predates this.
- 2019: Alaska's Valdez-Cordova Census Area was split into Chugach and Copper River, both with new codes.
- 2015: Shannon County, South Dakota became Oglala Lakota County, and because codes are assigned alphabetically the code changed with it. Wade Hampton Census Area in Alaska became Kusilvak the same year.
- 2013: Three Alaska entities changed shape while keeping their identifiers, and Bedford city, Virginia reverted to a town inside Bedford County and left the county list entirely.
The pipeline validates against the current vintage on every run and fails loudly if the county universe changes, rather than letting a new or retired entity slip through unnoticed.
Checking what you are reading
Every data page carries a source line naming the product and its release date, and a rebuild date at the foot. If a figure here disagrees with another source, compare the vintages first: that is the explanation more often than not.Why three Census figures for the same county disagree explains the three products and what each one measures.